A venipuncture procedure, particularly when used to insert a peripheral intravenous line in a patient, may be painful for the patient. In many instances, the procedure may have to be repeated multiple times before successful insertion of a peripheral line. Repeated probing may result in swelling or bulging veins.
Venipuncture often employs hypodermic needles. Hypodermic needles are normally made from a stainless-steel tube. The end of a hypodermic needle is typically beveled to create a sharp point at the distal tip. The sharp point at the distal tip allows the needle to easily penetrate the skin of the patient. The diameter of a hypodermic needle is indicated by a needle gauge. Various needle lengths are available for any given needle gauge. There are a number of systems for gauging needles, including the Stubs Needle Gauge and the French Catheter Scale. Needles in common medical use range from 7 gauges (the largest) to 33 gauges (the smallest) on the Stubs scale.
An intravenous cannula or catheter is a flexible tube that is generally plastic, such as polyurethane or silicon. The intravenous cannula or catheter typically has a trocar or stylet that, when inserted into the body, is used either to withdraw fluid or insert medication. Cannulae normally come with a trocar or stylet attached that punctures the body to get into the intended space. The trocar or stylet is generally removed once the cannula is in position. A small amount of blood appearing at the back of the needle signals a successful piercing of a vein. Use of a trocar or stylet may be hazardous to one's health. For example, an accidental stick needle injury may cause transmission of hepatitis, AIDS, or other hazardous condition.
A sharp distal end of the trocar is inserted inside the vein lumen with the tip of the cannula. After backflow of blood is detected, the trocar may be pulled slightly in a proximal direction and the cannula pushed slightly in a distal direction. The pulling and pushing may be repeated until the main trunk of the cannula is introduced into the vein lumen and the trocar is completely removed from the vein lumen.